NIRS

GLM or Block Average

Functional connectivity

Brain activity -> “stimulus/(or task)-evoked hemodynamic response”

fNIRS signal is a combination of

(i) evoked neurovascular coupling by a stimulus/ task

(ii) non-evoked (i.e. spontaneous) neurovascular coupling

(iii) processes that are not induced by neurovascular coupling

The signals measured by fNIRS and other modalities (e.g. fMRI) are contaminated with signal components that are not associated with functional brain activity, which may mask the brain activity

Data acquisition

As a second component (SC4), spontaneous brain activity (i.e. non-evoked) is also associated with neurovascular coupling and contributes to the variability of fNIRS signals. This component can be used to assess the so called “resting-state functional connectivity” of the brain

• Data we aquiere it is not only of brain
• Vasomotor waives (<=o.1Hz)
• Respiration f(=0.2Hz)
• Cardiac (=1Hz)
• Measurement noise
• Mayer Waves (blood pressure waves =0.1Hz)
• Machine drift (Its recommended that you turn on the NIRS equipment several minutes before data collection, so we could avoid having drifts-noise).

Measurement Noise

& other factors

“continuous wave” means that the instrumentation is solely based on a light intensity measurement.

Two of a few more discrete wavelengths

[HbO] and [HbR] cannot be determined absolutely in CW systems. However, with a few reasonable assumptions it is possible to quantify changes in HbO] and [HbR].

“quantification is not that important in neuroscience, i.e. it is more important to statistically significantly detect a change in brain activity than to quantify it in absolute terms”.

• Most imaging systems are based on CW technology.

• Time resolved systems have a lower time resolution, are more expensive and the time of flight is generally a more noisy parameter than the intensity and therefore not useful for detecting small functional activations.

• CW systems are relatively low cost, can be miniaturized and wireless systems and can be applied unobtrusively in everyday life situations or even freely moving animals.

• It could be generated white noise of the enviroment
• We could have Physiological contamination as light, movements, noise, etc.
• And another thing to be consider is:

*Another strong argument for our research in women.

fNIRS

Functional Near Infrared Spectroscopy

How Does it Work

BOLD response:

As neuron fire, they consume metabolic resources as O2, wich takes a ride on proteins alled hemoglobin to activation zone.

They have different absorption spectra. Using this fact, we could detect when HbO concentration is changing.

NIRx wavelengths: 760nm and 850nm

Montagem

• That activity generates an Hemodinamic Response, allowing NIRS to record those changes
• Light get through some tissues without a problem as skin and bone but its different between HbO and Hb

• It depends on what you want to research.
• It uses the international 10-5 position system
• Measures are done as on EEG or tDCS. Inion-Nasion & Tragus.
• Depends on the settings of study, we set up the cap configuration
• Our study uses 4 sources and 18 detectors, due to our objective.

NIRS EVOLUTION

1940

1977

• Francis Jobsis was the first to use NIRS to measure cortical oxygenation in Humans

• Glen Mellikan delovepes pulse oximetry to detect Blood Oxigenation in Fighter Pilots

1977

1940

1989

1988

It´s a non Invasive Neuro Image Device

• Delpy et al. developed modify BEER LAMBER LAW to help quantify brain activity changes

• First commercial system sold by Hamamatsu Photonics

1988

1989

- Functional means that it takes a lot of pictures of the brain over time to identify changes in Activity.

- Related to blood flow on the brain

- OPTODES = Emit\Collect light (Source-Detector)

Why we use it ?

fNIRS 101

An introduction to a non Invasive neuro imaging technique.